Z-scheme Charge Separation Research Articles

Direct Z-scheme 1D/2D WO2.72/ZnIn2S4 hybrid photocatalysts with highly-efficient visible-light-driven photodegradation towards tetracycline hydrochloride removal

There are increasing environmental concerns of serious pollution from emission of antibiotic wastewater. Herein, a series of direct Z-scheme WO2.72/ZnIn2S4 (WOZIS) hybrid photocatalysts composed of one-dimensional (1D) WO2.72 (WO) nanorods and two-dimensional (2D) ZnIn2S4 (ZIS) nanosheets have been designed and constructed for tetracycline hydrochloride (TCH) degradation without presence of solid-state electron mediators. The crystalline phase, chemical composition, morphology, optical properties and photocatalytic activity of the as-prepared samples were characterized by the XRD, XPS, SEM, HRTEM, BET, UV–vis DRS, and PL. Obviously, all the WOZIS hybrid photocatalysts exhibited significantly enhanced photocatalytic activity towards TCH degradation. Meanwhile, WOZIS-1 sample with WO/ZIS molar ratio of 1:1 showed the highest photocatalytic activity. The significantly enhanced photoactivity of WOZIS hybrid photocatalyst was due to Z-scheme charge separation mechanism based on the build of tight interfacial contacts between WO nanorods and ZIS nanosheets, thereby driving efficient charge separation. Moreover, the high photocatalytic stability of as-prepared WOZIS-1 hybrid sample was revealed through seven successive cycling reactions.

Preparation and characterization of novel Ag/Ag2WO4/ZnWO4 heterojunctions with significantly enhanced sunlight-driven photocatalytic performance

In this paper, a series of Ag/Ag2WO4/ZnWO4 heterojunction photocatalysts were fabricated by a facile hydrothermal method. The specific surface area, structure, morphology and separation rate of photo-induced charge pairs of the as-prepared heterojunction photocatalysts were characterized by various experimental methods. The photocatalytic performance of heterojunction photocatalysts was evaluated by decolorization of rhodamine B (RhB) aqueous solution under simulated sunlight irradiation. The results reveal that Ag/Ag2WO4/ZnWO4 heterojunction photocatalysts exhibit higher specific surface area, separation efficiency of photo-induced charge pairs and photocatalytic performance than that of the reference ZnWO4. The photocatalytic evaluation results further illustrate that the sample with a molar ratio of Ag/Zn = 2% holds the highest activity. The trapping and ESR experiments illustrate that O2− is primary active free radicals in the degradation process of RhB, which can be attributed to the presence of Ag0 in the heterojunctions. According to all the experimental results, a Z-scheme charge separation and transfer mechanism has been proposed to explain the relationship between the enhanced photocatalytic performance and the photoinduced carrier's separation and transfer process of Ag/Ag2WO4/ZnWO4 heterojunction photocatalyst.

0D/2D Z-scheme heterojunctions of g-C3N4 quantum dots/ZnO nanosheets as a highly efficient visible-light photocatalyst

Constructing Z-scheme heterojunctions comprising of constituents with different dimensionality is an effective strategy to spatially separate electron and hole. To fully utilize the synergistic coupling effect of dimensionality, herein, we first immobilize g-C3N4 quantum dots (CNQDs) onto ZnO nanosheets with oxygen vacancies (OV-ZnO) to create a 0D/2D hybrid via a facile and cost-effective approach. The CNQDs/OV-ZnO heterojunctions display CNQDs content-dependent performance in visible-light photocatalytic activity. The optimal CNQDs/OV-ZnO heterojunction exhibits high photocatalytic activity for degradation of methyl blue and bisphenol A, where the kinetic constant is 11.4 and 32.5 fold of pure OV-ZnO, respectively. Photoluminescence, electrochemical impedance spectroscopy and photocurrent verify that the photogenerated electron-hole pairs in this 0D/2D Z-scheme heterojunction have been effectively separated. The enhanced photocatalytic activity could be attributed to the synergistic effect of efficient Z-scheme charge separation, highly dispersed 0D CNQDs, coordinating sites of 2D OV-ZnO nanosheets and the strong coupling between them. In addition, the 3D flower-like structure constructed by 2D nanosheets greatly inhibits the leaching and loss of the photocatalyst in the recycling process, and ensures the high recycling ability of CNQDs/OV-ZnO. This work paves the way toward designing novel visible-light 0D/2D photocatalysts in the application of solar energy.

Z-Scheme Charge Separation in Bi24O31Br10/SrTiO3 Nanocomposites for Degradation of Methyl Orange

Promising mesoporous Bi24O31Br10/SrTiO3 (BOB/STO) nanocomposites were successfully designed and fabricated via a three-step approach. The morphology, structure, optical performance, surface area and pore-size distribution of the products were characterized by x-ray powder diffraction, x-ray photoelectron spectroscopy, field-emission scanning electron microscopy, transmission electron microscopy, energy-dispersive x-ray spectroscopy, diffuse reflectance spectroscopy and Brunner–Emmett–Teller analysis. The results indicate that BOB/STO nanocomposites are composed of perovskite STO nanoparticles and monoclinic BOB nanosheets. Compared with pure STO nanoparticles or BOB nanosheets, the mesoporous BOB/STO nanocomposites show a much better photocatalytic activity for the removal of methyl orange solution under simulated sunlight irradiation. In particular, the 10% BOB/STO composite is found to be the optimal composite, over which the dye decomposition reaches 95.3% for 100 min. The photocatalytic decomposition rate of the 10% BOB/STO nanocomposite is found to be 3.4 and 4.09 times higher than that of bare BOB and STO, respectively. The enhanced photocatalytic performance of the BOB/STO nanocomposites is attributed to the efficient charge separation and reduced recombination probability of photogenerated electron–hole (e−–h+) pairs. Furthermore, the BOB/STO nanocomposites show the considerable stability and recycling capacity in the reaction process. In addition, the photocatalytic mechanism of the BOB/STO nanocomposites is explained by a plausible Z-scheme heterojunction.

Design and Comparative Studies of Z-Scheme and Type II Based Heterostructures of NaNbO3/CuInS2/In2S3 for Efficient Photoelectrochemical Applications

Here, we report the fabrication of a new Z-scheme based core/shell/shell heterostructure of NaNbO3/CuInS2/In2S3 (core/shell/shell) for photoelectrochemical (PEC) water splitting and also for degradation of organic pollutants. We have also performed a comparative study with a modified heterostructure of NaNbO3/In2S3/CuInS2 having Type II band alignment. The PEC measurements under visible light irradiation show increased photocatalytic performance for the NaNbO3/CuInS2/In2S3 heterostructures as revealed by a high current density of ∼6.72 mA/cm2 at -1.0 V versus Ag/AgCl and low photocurrent onset potential of ∼ -110 mV in comparison to the Type II system (∼1.63 mA/cm2 and -180 mV vs Ag/AgCl). Mott-Schottky plots confirmed the n-p-n type heterojunction formation in the NaNbO3/CuInS2/In2S3 heterostructure which reduces the charge carrier recombination (revealed by PL intensity and short lifetime). The Z-scheme based system also exhibits excellent degradation efficiency (∼99.6%) of organic pollutants. This work shows that the Z-scheme charge separation mechanism in NaNbO3/CuInS2/In2S3 nanostructures is more efficient than the Type II based on NaNbO3/In2S3/CuInS2.

Architecture of high efficient zinc vacancy mediated Z-scheme photocatalyst from metal-organic frameworks

Direct Z-scheme composite is an ideal system for photocatalytic H2 production, which can efficient separation photo-induced charges and maintain stronger redox ability. Herein, we developed a facile method to fabricate Zn-vacancy mediated direct Z-scheme CdS/ZnS composites derived from CdS/MOF-5 via using Na2S and Na2SO3 aqueous solution as sacrificial agent in the process of photocatalytic reaction. XPS and PL results demonstrated that the metal-organic frameworks (MOF-5) transformed ZnS possesses abundant zinc vacancies, which help to form ohmic contact and broaden light absorption. Upward PL certifies the two-photons absorption behavior of the zinc vacancies ZnS under visible-light irradiation. Benefited from the ohmic contact which is inducted by zinc vacancy defects, the photo-induced electron of ZnS on the zinc vacancy defect level recombine with the holes of CdS in VB though the ohmic contact. As a result, the electrons and holes of CdS in the VB and CB can be efficiently separation and the photocorrosion is effectively suppressed, leading to drastically enhanced photocatalytic H2 evolution performance. The maximum photocatalytic H2 production rate of 11.62 mmol h−1 g−1 is obtained with an apparent quantum efficiency of 11.09% at 470 nm over CdS/MOF-5(25) heterojunction without any noble-metal as cocatalyst in Na2S and Na2SO3 aqueous solution, which is about 89.38 and 31.4 times greater than that of the bare MOF-5 and CdS, respectively. Moreover, S 2p XPS spectra of recyclability testing CdS/MOF-5(25) sample and the time-resolved fluorescence (TRPL) decay further prove the Z-scheme charge transfer and separation mechanism. This work represents a simple strategy to fabricate visible-light responded Zn-vacancy ZnS derived from MOF-5 and highlights the critical role of defects for developing Z-scheme photocatalyst in solar energy conversion.

Bi SPR-Promoted Z-Scheme Bi2MoO6/CdS-Diethylenetriamine Composite with Effectively Enhanced Visible Light Photocatalytic Hydrogen Evolution Activity and Stability

Recently, CdS has been intensively investigated for its excellent photocatalytic hydrogen (H2) evolution property. However, the poor stability and serious photocorrosion severely influence its potential for practical application. In this work, we successfully synthesized Bi surface plasmon resonance (SPR)-promoted Z-scheme Bi2MoO6 nanosheet/CdS-diethylenetriamine (Bi–Bi2MoO6/CdS-DETA) composites via an in situ solvothermal method. Crystalline structure, morphology, electrochemical properties, along with the photocatalytic H2 evolution activity and stability, have been systematically investigated. The as-prepared Bi–Bi2MoO6/CdS-DETA composites with optimized structure exhibited advanced photocatalytic H2 evolution activity (reach to 7.37 mmol h–1 g–1) and high stability. Largely exposed active sites, effective Z-scheme charge separation and Bi metal SPR effect of the two-dimension (2D) heterostructure is contributed to improve H2 generation performance of Bi–Bi2MoO6/CdS-DETA composites. This work provides ...

0D/2D Z-Scheme Heterojunctions of Bismuth Tantalate Quantum Dots/Ultrathin g-C3N4 Nanosheets for Highly Efficient Visible Light Photocatalytic Degradation of Antibiotics.

Constructing 0D/2D Z-scheme photocatalysts is a great promising path to improve photocatalytic activity by efficiently enhancing charge separation. Herein, we fabricated a visible-light-responsive Bi3TaO7 quantum dots (QDs)/g-C3N4 nanosheets (NSs) 0D/2D Z-scheme composite via a facile ultrasound method, and Bi3TaO7 QDs could be interspersed on the surface of g-C3N4 NSs uniformly. Furthermore, the strong interaction between Bi3TaO7 QDs and g-C3N4 NSs disturbed the CN heterocycles by forming C═O bonds between C atoms of the N-(C)3 group and O atoms of the Ta-O bond. The optimum composite with 20 wt % g-C3N4 NSs showed the superior photocatalytic activity for degradation of ciprofloxacin (CIP) over the composites prepared by mechanical mixing and solid-state methods, the photocatalytic efficiency of which were 4 and 12.2 times higher than those of bare Bi3TaO7 and g-C3N4. Photoluminescence (PL), time-resolved transient PL decay spectra, and photocurrent together verify that the photogenerated hole-electron pairs in this 0D/2D Z-scheme composite have been effectively separated. The enhanced photocatalytic activity of as-synthesized photocatalysts could be attributed to the synergistic effect of efficient Z-scheme charge separation, highly dispersed 0D Bi3TaO7 nanocrystals, coordinating sites of 2D g-C3N4 NSs and the strong coupling between them. This study might pave the way toward designing novel visible-light-induced 0D/2D photocatalyst systems for highly efficient degradation of antibiotics.

Preparation and characterization of CdS/BiOI composites with enhanced photocatalytic activity for degradation of 17α-ethinyl estradiol

A novel CdS/BiOI composite has been prepared via a chemical bath deposition method. The physical and chemical properties of as-prepared composites were characterized by XRD, SEM, TEM, EDS, XPS, UV–vis DRS, and PL. The synthesized CdS/BiOI composites exhibited superior photocatalytic activity in photodegrading of 17α-ethinyl estradiol (EE2) compared to pure CdS and pure BiOI, and the removal rate of EE2 could approach 100% after only 12 min of visible light irradiation using 3:1 CdS/BiOI composite as photocatalyst. The reaction rate constant over 3:1 CdS/BiOI composite was 6.3, 7.1 and 70.9 times higher than that of pure CdS, pure BiOI and P25 respectively. In addition, a Z-scheme charge separation mechanism was proposed on the basis of the experimental results and the theoretical calculation. Moreover, the prepared composite showed good stability and recyclability which are beneficial for its practical application.

Enhanced photocatalytic performance of Ag/AgCl/SnO2 originating from efficient formation of ·O2−

In this study, the Ag/AgCl/SnO2 composite photocatalysts with diffident molar ratios of Ag/Sn nanoparticles were facilely constructed by a precipitation method. The samples were characterized by X-ray diffraction patterns (XRD), UV-Vis diffuse reflectance spectra (DRS), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), electron spin-resonance (ESR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The Ag/AgCl/SnO2 composite with molar ratio of Ag/Sn = 7% display the highest photocatalytic activity under the simulated sunlight irradiation. The active free species trapping and NBT experiments indicate that the photo-induced charges separation and transfer result in the efficient formation of ·O2− in the composite system. Based on all the experimental results, a Z-scheme charge separation and transfer mechanism was proposed to explain the efficient formation of ·O2− over Ag/AgCl/SnO2 composites under the simulated sunlight irradiation.

Constructing Z-scheme charge separation in 2D layered porous BiOBr/graphitic C3N4 nanosheets nanojunction with enhanced photocatalytic activity

In the present work, a series of layered BiOBr/g-C3N4 heterojunction photocatalysts were prepared via a simple reflux process, and their photocatalytic performance was investigated by the degradation of rhodamine B (RhB) and bisphenol A (BPA) under visible light irradiation. It was found that BiOBr nanoplates were deposited on the external surface of g-C3N4nanosheets (CNNS) and the tightly contacted interface was formed between two components, giving rise to a 2D porous layered heterojunction structure with a high specific area. It was found that BiOBr nanoplates coupled with the proper amount of CNNS exhibited an excellent photocatalytic performance due to the combined effects of layered heterojunction, high specific surface area and porous structure, which lead to the high efficiency of light harvesting and charge separation. The active species of OH is the most crucial one while h+ and O2−contributed to a lesser extent in RhB and BPA photocatalytic degradation. Based on the direct evidence of the formed OH, O2− and h+ active species detected by active species capture experiment and ESR spectra, a Z-scheme photocatalytic mechanism was proposed for the charge separation. The present work may provide an insight for designing novel layered Z-scheme heterojunction photocatalysts with a high performance.

Enhanced photocatalytic inactivation of Escherichia coli by a novel Z-scheme g-C3N4/m-Bi2O4 hybrid photocatalyst under visible light: The role of reactive oxygen species

Biohazards are widely present in wastewater, and contaminated water can arouse various waterborne diseases. Therefore, effective removal of biohazards from water is a worldwide necessity. In this study, a novel all-solid-state Z-scheme g-C3N4/m-Bi2O4 heterojunction was constructed using a facile hydrothermal approach. Using the optimum g-C3N4/m-Bi2O4 (1:0.5), 6 log10 cfu/mL of E. coli K-12 could be completely inactivated within 1.5h under visible light irradiation, while only 1.2 log10 cfu/mL and 3.2 log10 of E. coli K-12 were inactivated by pure g-C3N4 and Bi2O4 under the same experimental conditions respectively. Emphasis was placed on identifying how the charge transfers across the g-C3N4/m-Bi2O4 heterojunction and a Z-scheme charge transfer mechanism was verified by reactive species trapping and quantification experiments. The Z-scheme charge separation within g-C3N4/m-Bi2O4 populated electrons and holes into the increased energy levels, thereby enabling one-step reduction of O2 to H2O2 and facilitating more generation of holes. This greatly accelerated photocatalytic efficiency on the inactivation of E. coli. Moreover, microscopy images indicate that cell structures were damaged and intracellular components were leaked out during the photocatalytic inactivation process. This study suggests that the newly fabricated Z-scheme g-C3N4/m-Bi2O4 is a promising photocatalyst for water disinfection.

Z-scheme CdS/g-C3N4 composites with RGO as an electron mediator for efficient photocatalytic H2 production and pollutant degradation

We herein report a novel ternary CdS/reduced graphene oxide (RGO)/graphitic carbon nitride (g-C3N4) hybrid photocatalyst for H2 generation and degradation of atrazine (a potent herbicide) through Z-scheme electron transport. Based on energy band theory, two visible-light-active semiconductors, CdS-coupled RGO and exfoliated g-C3N4 nanosheets (NSs), were coupled to construct Z-scheme hybrids using a hydrothermal process. Compared with the bare photocatalysts, the as-prepared hybrid photocatalysts exhibited efficient H2 generation and atrazine degradation activity owing to improved charge separation and photostability. As the electron mediator, RGO played an important role in accelerating electron transfer at the CdS/g-C3N4 interface via the Z-scheme electron transfer pathway. This Z-scheme charge transfer was verified using various techniques, including photoluminescence, transient photocurrent measurements, and determination of the photocatalyst band potentials. A suitable Z-scheme charge separation mechanism was proposed for the improved H2 generation activity. The intermediates formed during atrazine decomposition were identified, and an explanation for the fragmentation pattern was proposed. The Z-scheme process confers improved charge separation and long-term photostability on the system, and provides new insights for the design of redox-mediator-free RGO-based Z-scheme composites for photocatalysis applications.

Enhanced visible light photocatalytic H2 production over Z-scheme g-C3N4 nansheets/WO3 nanorods nanocomposites loaded with Ni(OH)x cocatalysts

Novel WO3/g-C3N4/Ni(OH)x hybrids have been successfully synthesized by a two-step strategy of high temperature calcination and in situ photodeposition. Their photocatalytic performance was investigated using TEOA as a hole scavenger under visible light irradiation. The loading of WO3 and Ni(OH)x cocatalysts boosted the photocatalytic H2 evolution efficiency of g-C3N4. WO3/g-C3N4/Ni(OH)x with 20 wt%defective WO3 and 4.8 wt%Ni(OH)x showed the highest hydrogen production rate of 576 μmol/(g–h), which was 5.7, 10.8 and 230 times higher than those of g-C3N4/4.8 wt%Ni(OH)x, 20 wt%WO3/C3N4 and g-C3N4 photocatalysts, respectively. The remarkably enhanced H2 evolution performance was ascribed to the combination effects of the Z-scheme heterojunction (WO3/g-C3N4) and loaded cocatalysts (Ni(OH)x), which effectively inhibited the recombination of the photoexcited electron-hole pairs of g-C3N4 and improved both H2 evolution and TEOA oxidation kinetics. The electron spin resonance spectra of •O2− and •OH radicals provided evidence for the Z-scheme charge separation mechanism. The loading of easily available Ni(OH)x cocatalysts on the Z-scheme WO3/g-C3N4 nanocomposites provided insights into constructing a robust multiple-heterojunction material for photocatalytic applications.

Highly enhanced photocatalytic degradation of methylene blue over the indirect all-solid-state Z-scheme g-C3N4-RGO-TiO2 nanoheterojunctions

In the present research work, the ternary indirect all-solid-state Z-scheme nanoheterojunctions, graphitic-C3N4/reduced graphene oxide/anatase TiO2 (g-C3N4-RGO-TiO2) with highly enhanced photocatalytic performance were successfully prepared via a simple liquid-precipitation strategy. The photocatalytic activities of indirect all-solid-state Z-scheme g-C3N4-RGO-TiO2 nanoheterojunctions were evaluated by the degradation of methylene blue (MB). The results showed that the introduction of RGO as an interfacial mediator into direct Z-scheme g-C3N4-TiO2 nanocomposites can remarkably enhance their photocatalytic activities. The as-obtained indirect all-solid-state Z-scheme g-C3N4-RGO-TiO2 nanoheterojunctions, with the optimal loading amount of 10wt% RGO, exhibited the highest rate towards the photocatalytic degradation of MB under simulated solar light irradiation. The degradation kinetics of MB can be described by the apparent first-order kinetics model. The highest degradation rate constant of 0.0137min−1 is about 4.7 and 3.2 times greater than those of the pure g-C3N4 (0.0029min−1) and direct Z-scheme g-C3N4-TiO2 (0.0043min−1), respectively. An indirect all-solid-state Z-scheme charge-separation mechanism was proposed based on the photoluminescence spectra and the trapping experiment procedure of the photo-generated active species. It was believed that the indirect all-solid-state Z-scheme charge separation mechanism in g-C3N4-RGO-TiO2 nanoheterojunctions could lead to the promoted charge separation and transfer, improved oxygen-reduction capacity of electrons in g-C3N4 and the formation of hydroxyl radicals driven by the holes in TiO2, respectively, thus achieving the highly enhanced photocatalytic degradation performance. This work might provide new insights and understanding on the graphene as electron mediators to design highly efficient all-solid-state Z-scheme nanoheterojunctions with enhanced visible-light driven photoactivity for various photocatalytic applications.

Oxygen defects-mediated Z-scheme charge separation in g-C3N4/ZnO photocatalysts for enhanced visible-light degradation of 4-chlorophenol and hydrogen evolution

g-C3N4 nanosheets were coupled with oxygen-defective ZnO nanorods (OD-ZnO) to form a heterojunction photocatalyst with a core-shell structure. Multiple optical and electrochemical analysis including electrochemical impedance spectroscopy, photocurrent response and steady/transient photoluminescence spectroscopy revealed that the g-C3N4/OD-ZnO heterojunction exhibited increased visible-light absorption, improved charge generation/separation efficiency as well as prolonged lifetime, leading to the enhanced photocatalytic activities for the degradation of 4-chlorophenol under visible-light illumination (λ>420nm). An oxygen defects-mediated Z-scheme mechanism was proposed for the charge separation in the heterojunction, which involved the recombining of photoinduced electrons that were trapped in the oxygen defects-level of OD-ZnO directly with the holes in the valence band of g-C3N4 at the heterojunction interface. The detection of surface generated reactive species including O2− and OH clearly supported the Z-scheme mechanism. Moreover, the g-C3N4/OD-ZnO photocatalysts also exhibited enhanced visible-light Z-scheme H2 evolution activity, with an optimal H2 evolution rate of about 5 times than that of pure g-C3N4. The present work not only provided an alternative strategy for construction of novel visible-light-driven Z-scheme photocatalysts, but also gained some new insights into the role of oxygen-defects of semiconductors in mediating the Z-scheme charge separation.

Tris-bipyridine based dinuclear ruthenium(ii)-osmium(iii) complex dyads grafted onto TiO2 nanoparticles for mimicking the artificial photosynthetic Z-scheme.

The Z-Scheme function within molecular systems has been rarely reported for solar energy conversion although it offers the possibility to achieve higher efficiency than single photon absorber photosystems due to the use of a wider range of visible light. In this study, we synthesized and investigated the electrochemical and spectroscopic properties of two new dyads based on ruthenium and osmium tris-bipyridine complexes covalently linked via a butane bridge to explore their ability to realize the Z-scheme function once immobilized on TiO2. These dyads can be grafted onto a nanocrystalline TiO2 film via the osmium complex bearing two dicarboxylic acid bipyridine ligands, while the ruthenium complex contains either two unsubstituted bipyridine ancillary ligands (RuH-Os) or two (4,4'-bis-trifluoromethyl-bipyridine) ancillary ligands (RuCF3-Os). Transient absorption spectroscopy studies of the Ru(ii)-Os(iii) dyads with femtosecond and nanosecond lasers were conducted both in solution and on TiO2. For both conditions, the photophysical studies revealed that the MLCT excited state of the ruthenium complex is strongly quenched and predominantly decays by energy transfer to the LMCT of the adjacent Os(iii) complex, in spite of the high driving force for electron transfer. This unexpected result, which is in sharp contrast to previously reported Ru(ii)-Os(iii) dyads, precluded us to achieve the expected Z-scheme function. However, the above results may be a guide for designing new artificial molecular systems reproducing the complex function of a Z-scheme with molecular systems grafted onto a TiO2 mesoporous film.

Removal of Nitric Oxide through Visible Light Photocatalysis by g-C3N4 Modified with Perylene Imides

For photocatalytic removal of nitric oxide (NO), two major issues need to be addressed: incomplete oxidation of NO and deactivation of the photocatalyst. In this study, we aimed to solve these two problems by constructing an all-solid-state Z-scheme heterojunction (PI-g-C3N4) consisting of g-C3N4 surface modified with perylene imides (PI). PI-g-C3N4 exhibits significant enhancement in photocatalytic activity (in comparison to pristine g-C3N4) when examined for NO removal. More importantly, the Z-scheme charge separation within PI-g-C3N4 populates electrons and holes into the increased energy levels, thereby enabling direct reduction of O2 to H2O2 and direct oxidation of NO to NO2. H2O2 can further oxidize NO2 to NO3– ion at a different location (via diffusion), thus alleviating the deactivation of the catalyst. The results presented may shed light on the design of visible photocatalysts with tunable reactivity for application in solar energy conversion and environmental sustainability.

BiVO4 nanowires decorated with CdS nanoparticles as Z-scheme photocatalyst with enhanced H2 generation

Highly efficient photocatalysts require to be achieved via an efficient charge separation action and responded under visible light. Here, we demonstrate a novel Z-scheme heterojunction photocatalyst composed of two visible light responding semiconductors without use of electron mediator. The as-prepared CdS nanoparticles decorated BiVO4 nanowires (CdS/BiVO4 NWs) exhibit broader light absorption region and Z-scheme charge separation mechanism for photocatalytic H2 generation under visible light. As a results, the optimizing CdS/BiVO4 NWs in 1:2wt ratio shows more than two times increase in photocatalytic H2 generation rate compared to bare CdS. Moreover, the Z-scheme CdS/BiVO4 NWs lead to main oxidation sites at BiVO4 NWs that successfully avoid photo-corrosion of CdS during photocatalysis.

Z-scheme TiO2/g-C3N4 composites with improved solar-driven photocatalytic performance deriving from remarkably efficient separation of photo-generated charge pairs

High recombination rate of electron-hole pairs and weak oxidation ability of holes from g-C3N4 greatly limit the catalytic degradation efficiency of g-C3N4-based photocatalysts, thus it is crucial to further improve the photocatalytic efficiency of g-C3N4. In this paper, TiO2 was successfully loaded onto the g-C3N4 surface to induce the electron−hole separation and enhance the photocatalytic efficiency. The results revealed the maximum photocatalytic performance toward discoloration of methyl orange (MO) aqueous solution under the simulated sunlight illumination at molar ratio of 3% TiO2 to g-C3N4 composite. The junction between TiO2 and g-C3N4 significantly accelerate the separation of the photo-generated charge pairs caused by the strong interactions between TiO2 and g-C3N4. Such highly efficient photo-generated charge separation can be explained by a Z-scheme charge separation and migration mechanism based on the results of the scavenger experiments and the energy band structures.